1. Field of the Invention
The present invention is directed to a twin-wire (i.e., a two-wire) former. More particularly, the present invention is directed to a twin-wire former used in the formation of a web of fibrous material from a fiber suspension, in particular as part of a paper production machine.
2. Discussion of the Background Information
German patent application 196 52 485.7 discloses a twin-wire former having two endless circulating wire belts or bands, which together form a twin-wire zone. The web of fibrous material forms between the twin-wire bands in the region of the twin-wire zone. At the twin-wire zone, the twin-wire bands move together over a forming roll, by which one wire band (the "inner wire band") comes into direct contact with the forming roll. At the reel-off point of the twin-wire bands from the forming roll, the other wire band (the "outer wire band") contacts at least one support device extending crosswise over the wire band, such as a skimmer. This skimmer may be rigidly attached to the frame of the machine or preferably) pressed against the outer wire band (for example, by a pneumatic hose). In each such embodiment, transitory divergence of the twin-wire bands (wire separation) is undesirable, and should be avoided using the skimmer at the reel-off point by applying tension to the wire bands in the direction of travel of the fiber web. However, divergence of the twin-wire bands is still occasionally observed, even though tension is applied as noted above. Such divergence disrupts the proper formation of the web.
By using a skimmer that can be pressed against the outer wire band, the position of the skimmer automatically adjusts to the actual layer thickness of the fiber suspension located between the twin-wire bands. A similar technique is shown in WO 95/34713. Nonetheless, disruptions of proper web formation are still observed in the finished web. For example, in a nonuniform basis weight-crosswise profile, the paper web makes a cloudy impression (on observation against a light source), whereby the cloudiness is sometimes strong and/or nonuniform. In other words, the quality of the "formation" is unsatisfactory.